The present invention relates to a device for rasping the intramedullary canal of a bone. The invention also concerns a method for manufacturing the device.
In articular arthroplasty, whatever the joint, there exist several types of prostheses which differ:
according to the pathology to be treated (trauma, arthrosis, malformation . . . ),
according to the state of health of the patient,
according to the type of approach first of all and the operating technique (anterior approach, posterior approach, with or without trochanterotomy . . . ),
able to bring about modifications with respect to:
the type of geometry of the prosthesis (self-blocking form or not, anatomic or straight, with or without supporting plate, ovoid or rectangular cross-section . . . ),
the type of fixation (with or without cement, with or without coating . . . ).
Surgeons need to adapt the preparation of the intramedullary canal of the bone depending on the type of prosthesis they will be using later, in order to operate efficiently and without risk, while still guaranteeing the reliability of the setting of the implant.
The medullary preparation or sizing of the bone is carried out using a broach. This shapes the intramedullary canal with precision so that the volume obtained corresponds with the volume of the implant to be set in place. In order to do this, the outer envelope of the broach is covered partially or totally by cutting teeth which will cut and consolidate the cancellous and cortical bone.
At present there are three families of cutting teeth more or less aggressive:
straight teeth,
straight teeth with chip breaker,
pyramid shaped diamond point teeth,
These different types of cutting teeth are more or less well adapted to the medullar sizing required by the surgeon depending on the type of prosthesis chosen.
For these different types of cutting teeth, it is possible to vary the parameters of the teeth: cutting angle, flat tooth summit, pitch, orientation of the teeth.
Furthermore, for pyramidal teeth, it is possible to vary the angle of inclination of the faces of the pyramid. The point of the pyramid can thus be oriented in opposition to the cut.
According to brevet U.S. Pat. No. 5,665,091 a broach is known for preparing the intramedullary canal of a bone intended to receive a prosthesis. This broach comprises a longitudinal axis and is constituted of an anterior face, a posterior face and two lateral faces, one internal and one external face, communicating with the internal walls of the canal. Each face of the broach is provided with different cutting teeth for preparing the canal. Certain types of teeth, such as those called diamond point, are arranged in parallel rows inclined relative to the longitudinal axis of the broach. The different cutting teeth have different efficiencies, that is to say that they are more aggressive or less aggressive. If the teeth are not very aggressive, they will have a compacting effect in the bone. On the other hand, if they are very aggressive, they will have a cutting effect in the bone. The most aggressive are the diamond point teeth. On this type of broach, each type of teeth is arranged on one face of the broach depending on the bone quality of the zone of the internal wall of the intramedullary canal with which this face of the broach is in contact.
The problem with this type of broach rests in the fact that the spread of teeth over the surface is not homogeneous. In fact, methods making it possible to produce the different types of teeth are limited and often they do not allow certain types of teeth to be generated in certain zones of the broach or else the shape of the teeth, in these zones, is no longer under control, for example at the junction between two faces. Thus, the efficiency and precision of the sizing are not guaranteed and there is a high risk of the broach breaking, from the concentration of stresses when in service.
The present invention therefore has the aim of compensating for these inconveniences of prior art by proposing a continuous machining method adapted to any shape whatever, making it possible to control the different types of teeth and the geometric properties of the teeth.
This aim is achieved by a machining method for obtaining cutting teeth on the surface of any shape whatsoever with a tool provided with a head, following at least one geometric curve traced on the envelope of said shape and having a helical form, characterised in that it comprises the following stages:
tracing the surface normal at a plurality of points taken along the helix,
making the helix follow the head of the tool, orienting the head in such a way that it follows the orientation of the defined normals.
According to another particularity, the machining is carried out with a tool having a head of bevelled shape.
According to another particularity, the machining is carried out following a low inclination helix, in order to obtain a teeth with the appearance of the straight teeth type.
According to another particularity, the machining is carried out to different depths following several helices with different inclinations respectively, in order to obtain a chip-breaker teeth.
According to another particularity, the machining is carried out following two helices with inverse pitches, in order to obtain teeth with a base of the spaces formed by the intersections of the two helices.
According to another particularity, the machining is carried out following the two helices at the same depth, in order to obtain a diamond point type teeth, the orientation of the teeth being normal to the envelope.
According to another particularity, the pitches of the two helices are constant and equal, in order to obtain teeth with the shape of regular pyramids.
According to another particularity, the two helices have different inclinations so that the teeth formed by the passage of the tool are not aligned.
According to another particularity, the pitch of each helix is constant along the envelope of any shape whatsoever.
According to another particularity, the teeth can be flat or splayed on their upper part, by including inside the profile of the bevelled head of the tool a plane or splayed part.
Another aim of the invention is to propose a broach, whose manufacture requires the implementation of the method described above, on which the mechanical stresses when in service are spread over the whole surface of the broach and on which it is possible to obtain a homogeneous spread of teeth.
In order to achieve this aim, one uses the method described above for shaping a broach intended to prepare the intramedullary canal of a bone so that it can receive a prosthesis, the broach comprising a body, elongated along an axis closely parallel to the longitudinal axis of the canal, a variable transversal section, constituted of a face called the upper face and an external envelope, and having a shape capable of communicating with the internal wall of the intramedullary canal of the bone.
According to another particularity, the body of the broach ends in a profiled shape to aid pushing the broach into the canal.
According to another particularity, male or female elements, arranged on the upper face of the body constitute a system of locking mechanisms intended to receive an end piece constituting the extremity of a handle to manipulate the broach in the canal and intended eventually to receive trial prosthetic components.
According to another particularity, the upper face of the body is plane or comprises a pin making it possible to weld a handle for manipulating the broach in the bone.